Comments on: Noise in Jones et al [1998]https://climateaudit.org/2005/09/25/noise-in-jones-et-al-1998/
by Steve McIntyreMon, 16 Oct 2017 21:49:47 +0000hourly1http://wordpress.com/By: David Stockwellhttps://climateaudit.org/2005/09/25/noise-in-jones-et-al-1998/#comment-37717
Tue, 04 Oct 2005 14:03:38 +0000http://www.climateaudit.org/?p=383#comment-37717Re: #34. A post on upsidedown quadratics would be great. The abundance of evidence that tree-ring growth does not have a ‘linear relationship with temperature’ as assumed by MBH98 should undermine any confidence in the conclusions of all methods using them, including the simple averaging advocated by Huybers.
]]>By: TCOhttps://climateaudit.org/2005/09/25/noise-in-jones-et-al-1998/#comment-37716
Fri, 30 Sep 2005 04:03:02 +0000http://www.climateaudit.org/?p=383#comment-37716You know this is not the first field in the world where people have worried about confounding factors (and a non-linear effect can be thought of as another factor, just adding in terms with higher orders in the polynomials and coefficients of their own). I think that is a pretty basic concept. Even one that a physicist would understand…let’s not keep acting like we discovered America with comments from the frigging peanut gallery. People like Stockwell acting as if it’s some concept Mann can not concieve of.

In any environmental or sociological study there are always worries about hidden factors, etc. (and limits to how many you can check.) The issue wrt Mann is to address their seriousness (within the grownups world of knowing this common concern). Not run around prattling 3 unknowns/2 equations like a simpleton.

I assume it’s ok to hit Dave, while letting Sid slide for 10 posts. Most sites I hang out at, I am the pet troll and allowed to be disruptive (double standard).

I’m thinking about another sabbatical or cutting back to weekly comments…

I’m going to post up on upside-down quadratics. We observed this in passing in our E&E article. The point seems so obvious and so unarguable that it’s remarkable that policy continues to be driven by tree rings.

When you add in the precipitation issues, it becomes like Monty Python. Half the proxies in MBH98 which are supposely temperature proxies are used in Cook et al [2004] as precipitation proxies.

]]>By: David Stockwellhttps://climateaudit.org/2005/09/25/noise-in-jones-et-al-1998/#comment-37714
Thu, 29 Sep 2005 22:45:16 +0000http://www.climateaudit.org/?p=383#comment-37714Sounds like the horns of a dilemma: admit the downturn is due to negative temperature correlation and the MWP goes up, or admit the downturn is due to falling temperatures and global warming goes down. Both unsatisfactory outcomes for the Hockey Team, or perhaps I am reading too much into it.
]]>By: ClimateAudithttps://climateaudit.org/2005/09/25/noise-in-jones-et-al-1998/#comment-37713
Thu, 29 Sep 2005 20:02:45 +0000http://www.climateaudit.org/?p=383#comment-37713I’ve seen a recent study under review in which they take their results up to 1985. They have ring widths in many sites up to 2000. The ring widths don’t go up after 1985; they decline. They report that the post-1985 verification fails. However, they get excellent verification in the late 19th century. So they exclude post-1985. Based on verification in a mid-19th-20th splits, they “confidently” make assertions about the relative level of the MWP to the late 20th century. I don’t think that they even realize what they’re doing.
]]>By: David Stockwellhttps://climateaudit.org/2005/09/25/noise-in-jones-et-al-1998/#comment-37712
Thu, 29 Sep 2005 17:14:05 +0000http://www.climateaudit.org/?p=383#comment-37712Steve, the work you are doing in exposing the flaws in MBH98 methodology is invaluable in preventing the endless repitition of similar flaws in the future, and perhaps a necessary step towards understanding the potential of tree rings to be proxies at all, with any methodology, with impacts on a wider class of studies. I think the assumption of “proxies following a linear temperature response” is wrong. The actual assumption for any workable proxy method based on instrument calibration at the recent end of the record, is a kind of homogeneity condition, that “proxies follow an identical linear temperature response to the calibration stage throughout the whole period and range of the proxy, and there is no other response to another confounding factor, such as precipitation, throughout the whole range”. Otherwise the proxy is varying in an unknown way to unknown factors. Commonsense would suggest this is far too strong a condition for growth of plants, but may be approximately met by quasi-physical proxies such as treelines, at least until trees reach the top of a mountain.

As an aside to the above, the Graybill-Idso sites may in fact have a linear temperature response, it is just that the CO2 or other response is stronger. So perhaps the reason sites should be rejected is not because they fail to meet MBH98 inadequately stated assumptions of linearity, but should be rejected because of a confounding factor.

Nevertheless, the conditions for success of tree ring proxies are much stronger than stated. It is not clear what the restated assumptions regarding linearity to one or more instrumental training patterns would entail, or if it is even a weaker condition than proxies following a linear temperature response. What I am saying is that irrespective of other flaws and problems of this particular study, the use of treegrowth as a proxy seems to be a very poorly specified model, that could only succeed under very limited conditions and would explain the general mess that the data show.

]]>By: Steve McIntyrehttps://climateaudit.org/2005/09/25/noise-in-jones-et-al-1998/#comment-37711
Thu, 29 Sep 2005 04:04:28 +0000http://www.climateaudit.org/?p=383#comment-37711David, this issue came up in our Nature submission, with an amusing response from Mann. We had written (and this particular claim carried over to our GRL submission although the rest of the article was recast)

Under MBH98 methodology, 16 overweighted sites (out of 70) account for virtually all the North American PC1 variance. All were high-altitude sites, mostly with cambial dieback (“strip-bark”) formation, showing very high 20th century growth rates. An unreported MBH98 calculation5, studying exclusion of these 16 and four other high-altitude sites, yielded a PC1 nearly identical to ours (Figure1c – correlation=0.95). 15 of these sites were collected by the same researcher (Donald Graybill). Graybill and Idso6 stated that their nonlinear growth rates could not be attributed to temperature and hypothesized direct CO2 fertilization. Hughes and Funkhouser7 called their growth rates a “mystery”. Mann et al.8 stated that their growth rates “are more dramatic than can be explained by instrumental temperature trends.” Since MBH98 methodology requires (p. 780) that proxies follow a linear temperature response, the Graybill-Idso sites should have been disqualified. Instead they were heavily overweighted.

Mann replied:

MM04 demonstrate their failure to understand our methods by claiming that we required that “proxies follow a linear temperature response”. In fact we specified (MBH98) that indicators should be “linearly related to one or more of the instrumental training patterns”, not local temperatures.

The idea that the Stahle/SWM network PC7 could have an intimate relationship with a temperatature PC11 is bizarre even for the Hockey Team, but that’s why they say.

]]>By: David Stockwellhttps://climateaudit.org/2005/09/25/noise-in-jones-et-al-1998/#comment-37710
Wed, 28 Sep 2005 18:42:32 +0000http://www.climateaudit.org/?p=383#comment-37710Re: #28 Yes that would be interesting. Another well known non-linearity from plant physiology is hysteresis in the growth response. E.g. plants can delay response to temperature as it increases, but continue responding as it falls – to avoid kind of being ‘faked out’ I guess. With all these non-linearites it would be useful to do some simulation to see what the possible linear range is. While MBH98 is to be applauded for attempting to state assumptions, in view of all the well known non-linearities in plant response, I wonder how one gets away with stating that non-linearity is a “relatively unlikely event”.

“[MBH98] The indicators in our multiproxy trainee network are linearly related to one or more of the instrumental training patterns. In the relatively unlikely event that a proxy indicator represents a truly local climate phenomenon which is uncorrelated with larger scale climate variations, or represents a highly nonlinear response to climate variations, this assumption will not be satisfied.”

]]>By: TCOhttps://climateaudit.org/2005/09/25/noise-in-jones-et-al-1998/#comment-37709
Tue, 27 Sep 2005 18:55:48 +0000http://www.climateaudit.org/?p=383#comment-37709RE 27: The way to do it (not sure if it is done, but just to show that it is possible) is to look at what the reconstruction gives you in temp changes, then see if those would be of the order to move you to the other side of the ecotone. For instance if the reconstruction shows a 1 degree change and the difference between ectones is 5 degrees (or maybe 2.5, gotta think about that), you are in good shape. (Yeah, you still might have some added noise if year to year variations are of the order of 5+ degrees, but even then you should be able to pull out signal, just maybe need to quantify the added uncertainty.)
]]>By: David Stockwellhttps://climateaudit.org/2005/09/25/noise-in-jones-et-al-1998/#comment-37708
Tue, 27 Sep 2005 17:16:42 +0000http://www.climateaudit.org/?p=383#comment-37708Re #25: inclusion trees at or near the optimum should cause cancellation in the average, they don’t actually have to be negative. Can you be sure all proxies are sited in the treeline ecotone, and remain there for their entire lifetime? After all, the main criterion for selection of proxies seems to be positive correlation with temperature, and these could be sited anywhere to one side of the response curve. Then, a warm period of sufficiently warmth, e.g. the MWP, could move positive growth responses into the optimal or even negative, depressing the overall signal, and flattening the apparent historic temperatures.
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